Standardize on 127.0.0.1 for oauth in dev

This addresses #1434. In development we use dev versions of our oauth
apps at Twitter, GitHub, and Bitbucket. Twitter doesn't allow us to use
localhost for the app location, but they do allow 127.0.0.1, which the
others allow as well. This standardizes on that so we have a consistent
experience in dev when working with multiple connected accounts.
Force 127.0.0.1:8537 to avoid localhost confusion

It's more normal to use localhost than 127.0.0.1, but Twitter won't let
us use localhost as the location or callback. We can use 127.0.0.1,
however, but since people are used to typing localhost let's redirect
them to 127.0.0.1 so they don't run into issues when they try to login
with our default dev oauth apps and land on a different host.
Use localhost:8537 as the CANONICAL_HOST after all

It turns out that when OAuth returns you to 127.0.0.1, if we have
CANONICAL_HOST set then you can be redirected--querystring intact--back
to localhost, with the result that the signing in works transparently.
Merge pull request #1454 from gittip/local-login

Standardize on 127.0.0.1 for oauth in dev